Polymer coated hydrolyzed membrane

Abstract

A method of forming a polymer coated hydrolyzed membrane includes forming a membrane from a first hydrophilic polymer by immersion precipitation, coating the membrane with a thin layer of a second hydrophilic polymer more pH tolerant than the first hydrophilic polymer to form a dense rejection layer, and exposing the coated membrane to a high pH solution thereby forming a hydrolyzed ultrafiltration membrane. A polymer coated hydrolyzed membrane includes a porous membrane formed from a first hydrophilic polymer by immersion precipitation and from hydrolysis, and a dense rejection layer applied to the membrane and formed from a second hydrophilic polymer more pH tolerant than the first hydrophilic polymer.

1 . A method of forming a polymer coated hydrolyzed membrane comprising:
 forming a membrane from a first hydrophilic polymer by immersion precipitation;   coating the membrane with a thin layer of a second hydrophilic polymer more pH tolerant than the first hydrophilic polymer to form a dense rejection layer; and   exposing the coated membrane to a high pH solution thereby forming a hydrolyzed ultrafiltration membrane.   
     
     
         2 . The method of  claim 1 , wherein forming a membrane from a first hydrophilic polymer comprises forming an asymmetric membrane by immersion precipitation comprising a solid skin layer and a porous support layer. 
     
     
         3 . The method of  claim 2 , wherein forming an asymmetric membrane by immersion precipitation comprises forming the solid skin layer comprising a thickness of about 5 to about 15 microns and the porous support layer comprising a thickness of about 20 to about 150 microns. 
     
     
         4 . The method of  claim 2 , wherein forming an asymmetric membrane by immersion precipitation comprises forming the solid skin layer comprising a density of polymer of about 50% or greater polymer by volume and the porous support layer comprising a density of polymer from about 15% to about 30% polymer by volume. 
     
     
         5 . The method of  claim 2 , wherein coating the membrane with a thin layer of a second hydrophilic polymer comprises coating the solid skin layer of the asymmetric membrane with a thin layer of a second hydrophilic polymer more pH tolerant than the first hydrophilic polymer to form a dense rejection layer. 
     
     
         6 . The method of  claim 2 , wherein forming an asymmetric membrane by immersion precipitation comprises forming an asymetric cellulose membrane from a hydrophilic cellulose ester polymer by immersion precipitation. 
     
     
         7 . The method of  claim 6 , wherein exposing the coated membrane to a high pH solution comprises exposing the asymetric cellulose membrane to a high pH solution thereby hydrolyzing a cellulosic portion of the asymetric cellulose membrane to form a hydrolyzed ultrafiltration membrane. 
     
     
         8 . The method of  claim 1 , wherein exposing the coated membrane to a high pH solution comprises exposing the coated membrane to a solution with a pH of about 12 or greater thereby forming a hydrolyzed ultrafiltration membrane 
     
     
         9 . The method of  claim 1 , wherein coating the membrane with a thin layer of a second hydrophilic polymer comprises coating the membrane with a 1 micron or less thick layer of a second hydrophilic polymer more pH tolerant than the first hydrophilic polymer to form a dense rejection layer. 
     
     
         10 . The method of  claim 1 , wherein coating the membrane with a thin layer of a second hydrophilic polymer comprises coating the membrane with a sulfonated polystyrene polyisobutylene block copolymer to form a dense rejection layer. 
     
     
         11 . A polymer coated hydrolyzed membrane comprising:
 a porous membrane formed from a first hydrophilic polymer by immersion precipitation and from hydrolysis, the membrane comprising a skin layer supported by a support layer; and   a dense rejection layer applied to the skin layer and formed from a second hydrophilic polymer more pH tolerant than the first hydrophilic polymer.   
     
     
         12 . The membrane of  claim 11 , wherein the membrane is an asymmetric membrane. 
     
     
         13 . The membrane of  claim 12 , wherein the asymmetric membrane comprises an asymmetric cellulose membrane formed from a hydrophilic cellulose ester polymer. 
     
     
         14 . The membrane of  claim 12 , wherein the skin layer comprises a thickness of about 5 to about 15 microns and the porous support layer comprises a thickness of about 20 to about 150 microns. 
     
     
         15 . The membrane of  claim 12 , wherein the skin layer comprises a density of polymer of about 50% or greater polymer by volume and the porous support layer comprises a density of polymer from about 15% to about 30% polymer by volume. 
     
     
         16 . The membrane of  claim 11 , wherein the dense rejection layer comprises a thickness of about 1 micron or less. 
     
     
         17 . The membrane of  claim 11 , wherein the dense rejection layer is formed from a sulfonated polystyrene polyisobutylene block copolymer.